Checking capacitors?

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Im trying to fix this cruise control on the Toyota, I hear that it's likely failing due to capacitors failing (keeping in mind I had to replace some to get my tachometer to work).

So here is my board

96feg08.jpg



So how would i check each of those capacitors? Im assuming (hoping) it'd be one of the barrel-shaped ones, which Ive replaced some of those before...but I dont know how to tell if one is bad or not.
 
It'll be cheaper to just replace them. They're electrolytics and probably cost $0.15 each (really!)

About the best you can do in most situations is to see if they're shorted by checking resistance across the two leads (both ways) with a VOM. USUALLY you'll see them charge when you have the VOM leads in one direction , and a short in the other. In-circuit like that though, it's tricky to test accurately.

If you could power the board up and measure the supply voltages around the board, that would be more fruitful. Those are generally used as filters and they fail short... but become resistors before they do. Their job is to pass AC voltage to ground and block DC voltage. They die much faster when they get hot. They get hot if there's a lot of AC on them (unlikely in your case) or when there's hot stuff around them (likely!). The problem is, a lot of these are in parallel , so it's tricky.

The little blue blobs are tantalum caps and can short too (they're a different type of electrolytic cap).

Do you have a schematic?

They're 30 yr old electrolytics in a harsh environement. They're on borrowed time.
 
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It'll be cheaper to just replace them. They're electrolytics and probably cost $0.15 each (really!)

About the best you can do in most situations is to see if they're shorted by checking resistance across the two leads (both ways) with a VOM. USUALLY you'll see them charge when you have the VOM leads in one direction , and a short in the other. In-circuit like that though, it's tricky to test accurately.

If you could power the board up and measure the supply voltages around the board, that would be more fruitful. Those are generally used as filters and they fail short... but become resistors before they do. Check and see if there's +5/+12 if you can

They're 30 yr old electrolytics in a harsh environement. They're on borrowed time.

There's an electronics shop nearby (WS), they're about a buck a pop - where can you find them for under a quarter?
 
I buy from Digikey. You'll spend $4.99 for shipping but they're going to be cheap. and arrive in 3 days or so. They come in 85 degrees C or 105 degrees C versions. The 105 degree parts last longer (especially in automotive) but either will work.
 
@JohnFreeman is right, it would be easier to replace all of them, that looks like a nice, spacious board for working. Are any of them slightly bulging at the top or leaking? I'm not sure that I've ever had one of those little thin film caps fail.
None look like it, but, then again, neither did the two I replaced on the tach.

Yeah, very little room to work and it'll be 'fun' figuring out which pins on the back align with them
 
None look like it, but, then again, neither did the two I replaced on the tach.

Yeah, very little room to work and it'll be 'fun' figuring out which pins on the back align with them

Oh, I wasn't being sarcastic about space. If you want awful, trying working on SMD chit. Just go slow and enjoy the solder fumes; they'll eventually lower your IQ enough to enjoy things like Rolling Rock beer and Florida Georgia Line.
 
Oh, I wasn't being sarcastic about space. If you want awful, trying working on SMD chit. Just go slow and enjoy the solder fumes; they'll eventually lower your IQ enough to enjoy things like Rolling Rock beer and Florida Georgia Line.
that explains so much about you... I'll pray for you
 
Yeah, very little room to work and it'll be 'fun' figuring out which pins on the back align with them

That's not a bad board to work on at all. The caps will be easy to locate on the rear. Treat it like graphing points on a grid. "this cap is 4 holes from the left side and 2 holes up from the bottom." flip it over and graph it out. Easy.
 
I used to do electronics repair. Agree on most points here in regards to the electrolytic caps, get the same cap from digikey or mouser and replace them all. Also, get a good light and magnifying glass and look for burns or anything odd. Look for cold solder joints.

Anything past that and your going to need quite a bit more time and thought. If worst comes to worst, try to bake it or hit the bay.
 
that explains so much about you... I'll pray for you

Gah, I said they lowered IQ, not made me gay enough to listen to bro country.

If you have micro flush cutters, you can just clip the leads on the cap side and heat up the trace on the opposing and they remnants of the lead will fall out.
 
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Agreed with all. That board is all thru-hole and wide open compared to what I usually have to put up with. No visible signs of cap failure, but you don't always have that. If you DO (i.e., the cap bulged or even burst), it often took something else with it, and then it gets...interesting.

Both Digi-Key and Mouser do same-day shipping, and parts get to you fast. I like Digi-Key's search engine better.

When buying replacements, there are a few peculiarities. Perversely, it may be cheaper to buy same footprint same capacitance but higher voltage for some of them. It all depends on the vintage of cap and what is available today.

If replacing all the caps doesn't fix it, let us know...for then the fun will begin...
 
Agree with all the above. As long as the capacitance value is correct, you can go up on the voltage rating, just don't go lower on the voltage rating. Map out the board. Pics and or a drawing are a must. Be sure and pay close attention to polarity, as those electrolytic caps are polarized. The tantalums also. I would do as suggested, and replace them all. Be sure and don't apply too much heat, as that can damage the traces and vias on the pcb. Take your time. Invest in a desoldering pump (solder sucker), and some solder wick, to clean up the through holes after you remove the parts.

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Gosh I love you guys, yall rule
 
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